Integrally fabricated micromachine and logic elements

ABSTRACT

Embodiments relate to micromachine structures. In one embodiment, a micromachine structure includes a first electrode, a second electrode, and a sensing element. The sensing element is mechanically movable and is disposed intermediate the first and second electrodes and adapted to oscillate between the first and second electrodes. Further, the sensing element includes a FinFET structure having a height and a width, the height being greater than the width.

RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 11/863,297 filed Sep. 28, 2007, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to micromachine structures. Moreparticularly, the invention relates to micromachine devices havingFinFET structures and integrated with CMOS logic.

BACKGROUND OF THE INVENTION

Today most discrete sensor elements in micrometer dimensions areproduced with special equipment and special processes. This results inboth cost disadvantages and difficulties producing large quantities ofhigh quality devices.

Integrated sensor systems implemented in 0.5-micrometer (um) logic areknown. In such integrated systems, the sensor element is manufactured ina separate process block. This also results in cost disadvantages.Further, the structure size and high mechanical sensitivity result inreduced robustness of the sensors in subsequent processing, treatment,and testing. For example, electrostatic forces can be used in testing.As a result of the structure size, however, required voltages are in therange of 5 volts (V) to 30V, incompatible with voltages in correspondinglogic processes and resulting in undesirable high current consumption.

SUMMARY

Embodiments of the invention are related to micromachine structures.

In an embodiment, a micromachine structure comprises a first electrode;a second electrode; and a mechanically movable sensing element disposedintermediate the first and second electrodes and adapted to oscillatebetween the first and second electrodes, the sensing element comprisinga forked fin FinFET structure having a height and a width, the heightbeing greater than the width.

In an embodiment, a micromachine structure comprises a first electrode;a second electrode; and a mechanically movable sensing element disposedintermediate the first and second electrodes and adapted to verticallyoscillate between the first and second electrodes, the sensing elementcomprising a FinFET structure having a height and a width, the heightbeing greater than the width.

In an embodiment, a micromachine structure comprises a positiveelectrode; a plurality of positive fins integrally fabricated with thepositive electrode and each cantilevered from the positive electrode ata first longitudinal end; a negative electrode arranged opposite thepositive electrode; and a plurality of negative fins integrallyfabricated with the negative electrode and each cantilevered from thenegative electrode at a first longitudinal end, the plurality ofnegative fins interleaved with the plurality of positive fins, acapacitance of the structure related to a relative distance between eachof the interleaved plurality of positive and negative fins.

In an embodiment, a method for fabricating a micromachine structurecomprises forming a first electrode; forming a second electrode; andintegrally forming a FinFET sensing element with the first and secondelectrodes in a FinFET fabrication process, the sensing elementcomprising a micromachine fin structure disposed intermediate the firstand second electrodes and adapted to oscillate between the first andsecond electrodes.

In an embodiment, a method for fabricating a micromachine structurecomprises forming a first electrode array; forming a second electrodearray; forming a FinFET sensing fin between the first and secondelectrode arrays on a sacrificial layer by etching away the sacrificiallayer while preserving the FinFET sensing fin; and providing a sealingfor the micromachine structure, the sealing substantially enclosing thefirst and second electrode arrays and the sensing fin.

In an embodiment, a micromachine structure comprises a first FinFETelectrode; and a second FinFET electrode spaced apart from the firstFinFET electrode and adapted to mechanically move into and out ofcontact with the first FinFET electrode, the first and second FinFETelectrodes comprising monocrystalline silicon fins each formed having aheight greater than a width.

The above summary of the invention is not intended to describe eachillustrated embodiment or every implementation of the present invention.The figures and the detailed description that follow more particularlyexemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood from the followingdetailed description of various embodiments in connection with theaccompanying drawings, in which:

FIG. 1 depicts a step of a process according to an embodiment of theinvention.

FIG. 2 depicts a step of a process according to an embodiment of theinvention.

FIG. 3 depicts a step of a process according to an embodiment of theinvention.

FIG. 4 depicts a step of a process according to an embodiment of theinvention.

FIG. 5 depicts a step of a process according to an embodiment of theinvention.

FIG. 6 depicts a step of a process according to an embodiment of theinvention.

FIG. 7 depicts a step of a process according to an embodiment of theinvention.

FIG. 8 depicts a step of a process according to an embodiment of theinvention.

FIG. 9 depicts a device according to an embodiment of the invention.

FIG. 10 is a top view of an oscillator according to an embodiment of theinvention.

FIG. 11 is a top view of an oscillator according to an embodiment of theinvention.

FIG. 12 is a top view of an oscillator according to an embodiment of theinvention.

FIG. 13A is a top view of an oscillator according to an embodiment ofthe invention.

FIG. 13B is a top view of an oscillator according to an embodiment ofthe invention.

FIG. 14A is a top view of an oscillator according to an embodiment ofthe invention.

FIG. 14B is a top view of an oscillator according to an embodiment ofthe invention.

FIG. 15 is a section view of an oscillator according to an embodiment ofthe invention.

FIG. 16 is a top view of an oscillator according to an embodiment of theinvention.

FIG. 17 is a top view of a variable capacity structure according to anembodiment of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments are related to micromachine structures and processes forproducing micromachine structures. Structures according to variousembodiments of the invention can provide full testability on-chip within-use voltages, with fabrication and processing of the chip compatiblewith standard processes. The invention can be more readily understood byreference to FIGS. 1-17 and the following description. While theinvention is not necessarily limited to the specifically depictedapplication(s), the invention will be better appreciated using adiscussion of exemplary embodiments in specific contexts.

FIGS. 1-8 depict a fabrication process of a micromachine structureaccording to one embodiment of the invention. According to oneembodiment of the invention, micromachine structures comprise sensorelements incorporating fin-type field effect transistor (FinFET)technology and comprising FinFET structures and can be produced as partof a FinFET fabrication process. As a result of the realization ofintegrated sensors and logic, large quantities of high quality devicescan be cost-effectively manufactured in a standard CMOS fabricationfacility, requiring no special equipment or disparate processes.Embodiments of the invention are also related to the use ofmonocrystalline silicon in the fabrication process.

In FIG. 1, the process can begin with a silicon on insulator (SOI)layered silicon-oxide-silicon substrate 100 in one embodiment. Substrate100 can include a bulk-Si layer 102, a buried oxide layer 104, and a Silayer 106 in various embodiments, and in one embodiment layer 104 canhave a thickness of about 150 nm and layer 106 about 90 nm.

In FIG. 2, fins 110 are formed in Si layer 106. In one embodiment, thewidth and pitch of fins 110 are less than about 100 nm. This small size,in addition to the narrow width of the final structure, makes possiblesmall deflections of large sensor signals. The structure also providesimproved mechanical characteristics, with increased robustness as aresult of low mechanical sensitivity. Improved mechanicalcharacteristics can also be provided in various embodiments through theuse of monosilicon as layer 106.

In FIG. 3, a sacrificial oxide fill layer 120 is added and planarizationis carried out.

Next, in FIG. 4, a cavity mask layer 130 is added. Layer 130 cancomprise polysilicon (poly-Si). In one embodiment, layer 130 has athickness of about 100 nm. In the step depicted in FIG. 5, a cavity mask132 is structured in layer 130.

In FIG. 6, the step of cavity corrosion is depicted. Cavity corrosionexposes fins 110 through oxide fill layer 120.

A cavity sealing step is depicted in FIG. 7. In this step, anoxide-sealing layer 140 is added over cavity layer 130. Metallizationand passivation steps are then carried out, as depicted in FIG. 8,adding layer 150.

According to embodiments of the fabrication process described above withreference to FIGS. 1-8, logic transistor structures and sensorstructures can be manufactured together, providing cost-effectiveintegrated sensor and logic elements. The logic can provide minimumstructures in the sub-100 nanometer (nm) range and has advantages forsensor integration, with respect to both cost over high integration ofseveral sensors and the technical performance of the individual sensors.Further, the dimensions of the structures make possible sensor actuationwith low voltages, compatible with customary CMOS technologies. Smalldimensioning also makes possible robust mechanical structures withcrucial advantages during the subsequent processing. One embodiment of aparallel-manufactured transistor 160 in depicted in FIG. 9.

Additionally, embodiments of the invention have reduced arearequirements for sensor structures with improved testability, aselectrostatic tests with available voltages are possible in a less thanabout 5V application area. Embodiments of the invention also facilitatedevelopment of new application ranges, which presuppose elements withminimum structure sizes, such as elements with low current consumptionby low voltages, oscillators with high frequency, and the like. Examplesinclude inertia sensors, capacitive and piezoresistive; accelerationsensors; gyrometers; PROM devices realized with cavity fuses;resonators; and variable capacitors, among others.

Examples of inertia sensors, resonators, and other devices will bedescribed with reference to FIGS. 10-17, which depict embodiments of amechanical oscillator according to the invention.

Referring to FIG. 10, one embodiment of a mechanical oscillator 200according to the invention comprises a movable bar element 202, a firstelectrode element 204, and a second electrode element 206. Oscillator200 further comprises a free corrosion area 208 in which movable barelement 202 is disposed. Bar element 202 is adapted to laterally ortransversely oscillate with respect to first electrode element 204 andsecond electrode element 206. First and second electrode elements 204and 206 can be gate electrodes, and although first electrode element 204is depicted as having a negative polarity, and second electrode element206 positive, the polarities can be reversed in other embodiments, asunderstood by those of skill in the art. In other embodiments, one offirst electrode element 204 and second electrode element 206 cancomprise an energizing electrode and the other can comprise a sensorelement.

FIG. 11 depicts another embodiment of an oscillator 210. Oscillator 210comprises movable element 212 having a dual bar, or tuning fork-like,geometry. Similar to oscillator 200 depicted in FIG. 10, movable element212 is disposed in a free corrosion area 218 between a first electrodeelement 214 and a second electrode element 216. The tuning fork geometryof element 212 can provide a stable and higher quality oscillator.

In FIG. 12, an oscillator 220 comprises a weighted movable element 222.Similar to other embodiments, weighted movable element 222 of oscillator220 is disposed intermediate first and second electrode elements 224 and226 in a free corrosion area 228.

As depicted, weighted movable element 222 comprises a mass 223 at adistal end. In other embodiments, weighted movable element 222 cancomprise alternate mass configurations, including alternate masspositions relative to proximate and distal portions of element 222 ortapering or expanding geometries. These and other various configurationsof weighted movable element 222 provide control of the frequency ofoscillation of oscillator 220 and therefore can be selected or tailoredfor particular applications and specifications.

FIGS. 13A and 13B depict further embodiments of mechanical oscillatorsaccording to the invention, in which gate electrodes 234 and 236 ofoscillator 230 are also free corroded, at 238. Additionally, gateelectrodes 234 and 236 can be doubly mounted at A and B, respectively,in contrast to embodiments previously depicted and described.

Further, dimensioning of movable element 232 can be varied, as depictedat 232 a in FIG. 13A and at 232B in FIG. 13B. The dimensions of movableelement 232, such as the length, can be varied according to a placementof moveable element 232 relative to energizing electrodes 234 and 236,for example. Additionally, a via hole of oscillator 230 can be placedbeneath electrodes 234 and 236 to facilitate minimum fin pitch.

Referring to FIGS. 14A and 14B, an embodiment comprising additionalelectrodes can provide higher harmonious oscillations. An oscillator 240comprises an oscillator element 242 disposed intermediate a plurality offin-structured gate electrodes 244 a. Electrodes 244 a are orthogonallyarranged in a 2.times.3 configuration relative to oscillator element 242and corroded region 248 in the embodiment depicted, although otherconfigurations are also possible.

In FIG. 14B, a similar configuration in another embodiment comprisespoly-silicon or metal gate electrodes 244. This embodiment additionallyprovides the orthogonal orientation that can transfer to existingtransistors.

A vertical configuration of an oscillator 250 according to an embodimentof the invention is depicted in FIG. 15. Such a configuration capturesvertical movement of movable element 252 by energizing electrodes 254.As in other embodiments, the polarities of electrodes 254 can also bereversed.

Another embodiment of an oscillator 260 shown in FIG. 16 can be used tocapture higher frequency oscillations. Oscillator 260 comprises amovable fin element 262 mounted at first and second ends in a corrodedarea 268 between first and second energizing electrodes 264 and 266.High frequency oscillations of an intermediate portion of element 262are registered by electrodes 264 and 266.

FIG. 17 depicts a variable capacitance structure 300, such as anelectrostatically adjustable capacitance varactor diode. Structure 300comprises a positive portion 302 and a negative portion 304, althoughthe polarities of portions 302 and 304 can be reversed in otherembodiments. A plurality of cantilevered fins 306 are disposed betweenboth and respectively coupled to one of portions 302 and 304, relativeto a clearance hole 308.

In structure 300, an overall capacitance is altered by creation of atension affecting fins 306 and therefore structure 300, wherein arelative distance between fins 306 affects the capacitance. Theresultant capacitance can be expressed ase.sub.0.times.e.sub.r.times.A/D, such that small changes are registeredexponentially. In one embodiment, this effect can be improved by coatingfins 306 with a material having a high e_(r).

One advantage of this embodiment is its breakdown voltage, which can bein the range of greater than 10V. Further, an activation voltage ofstructure 300 can be between about 2V and about 3V, with attainablecapacitances in the nano-Farad (nF) range and a difference betweenmaximum and minimum capacitances of about 3 to 4.

Various combinations of the embodiments depicted in FIGS. 10-17 are alsopossible according to the invention. The fins in various embodiments cancomprise pure silicon, heavily doped silicon, and/or silicidizedsilicon. If the CMOS process includes reduction of Ohmic resistance forthe reduction of the resistances in transistor connection areas beforethe growth of the epitaxial silicon, this process step can be blocked bya special mask, since thereby the geometrical dimensions of themechanical oscillator would change with respect to the corroded finstructure.

In another embodiment, a micromachine structure according to theinvention comprises two electrodes. One or both of the electrodes areadapted to mechanically move into and out of contact with the otherelectrode. Each of the electrodes can comprise a FinFET structure havinga height greater than a width in one embodiment, and the FinFETstructures can comprise silicon, such as monocrystalline silicon. Inthis and other embodiments described herein, the FinFET structures canbe formed as part of a standard FinFET fabrication process on bulk oroxide, such as a buried oxide, and can be formed on a sacrificial layerwhich can be etched away while preserving the FinFET structures.

Embodiments of the invention are thus related to the use ofmonocrystalline silicon in the fabrication of micromachine structures,such as sensor elements, produced in a CMOS multi-gate technology, suchas FinFET. Use of FinFET processes, for example, provides advantages notavailable with traditional micromachining processes. The invention canprovide smaller but more robust mechanical and electrical structurescapable of handling in-use test voltages, the result of which arehigh-quality structures which are easily fabricated, processed, sealedand packaged, and tested. For example, smaller micromechanicalstructures according to embodiments of the invention require smallervoltages, enabling the structures to be integrated in test procedures atin-use voltages less than about 5 V, such as about 2V to about 4V invarious embodiments. The smaller structures, in one embodiment, canreduce a gap requirement for the sensing or oscillating fin from about0.5 um to less than about 100 nm, for example about 20 nm to about 60nm. In other embodiments, the gap can be less than about 20 nm, forexample about 15 nm, with the area requirement correspondingly beingreduced by a factor of about 10. The smaller structures, however, arestill more robust, providing reasonable signals with only smalldeformations.

Although specific embodiments have been illustrated and described hereinfor purposes of description of an example embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations calculated to achieve thesame purposes may be substituted for the specific embodiments shown anddescribed without departing from the scope of the present invention.Those skilled in the art will readily appreciate that the invention maybe implemented in a very wide variety of embodiments. This applicationis intended to cover any adaptations or variations of the variousembodiments discussed herein, including the disclosure information inthe attached appendices. Therefore, it is manifestly intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method for fabricating a micromachine structurecomprising: forming a first electrode; forming a second electrode; andintegrally forming a FinFET sensing element with the first and secondelectrodes in a FinFET fabrication process, the sensing elementcomprising a micromachine fin structure disposed intermediate the firstand second electrodes and adapted to oscillate between the first andsecond electrodes.
 2. The method of claim 1, further comprising testingthe micromachine structure using in-use voltages.
 3. The method of claim1, further comprising activating the sensing element with a voltage ofless than about 5 V.
 4. The method of claim 1, wherein forming the firstand second electrodes is carried out such that a gap between the firstand second electrodes is about 20 nm to about 60 nm.
 5. A method forfabricating a micromachine structure comprising: forming a firstelectrode array; forming a second electrode array; forming a FinFETsensing fin between the first and second electrode arrays on asacrificial layer by etching away the sacrificial layer while preservingthe FinFET sensing fin; and providing a sealing for the micromachinestructure, the sealing substantially enclosing the first and secondelectrode arrays and the sensing fin.